class_docstr: Samples elements from a Dataset for which `fn` returns True.
  
  Parameters
  ----------
  fn : callable
      A callable function that takes a sample and returns a boolean
  dataset : Dataset
      The dataset to filter.
code: def __init__(self, fn, dataset):
      self._fn = fn
      self._dataset = dataset
      self._indices = [
          i for i, sample in enumerate(dataset) if fn(sample)
      ]
  
imports: import numpy
label_desc: Use image node_id 1 to create a new FilterSampler object from inherited base classes: Sampler with example: obj = FilterSampler(fn, dataset)